An exhaust system usually comprises at least one exhaust tract, which has at least one exhaust pipe which guides exhaust gas. The respective exhaust tract is used to discharge exhaust gas which is produced in the combustion chambers of the internal combustion engine. Depending on the size of the internal combustion engine, the exhaust system manages with a single exhaust tract or comprises at least two exhaust tracts, for example in the case of a V engine. Exhaust gas treatment devices are usually arranged in the respective exhaust tract, such as catalysts, particle filters, SCR systems and silencers, which are connected to each other by means of exhaust pipes. An exhaust tract usually comprises an exhaust manifold on the input side, while an end pipe, what is known as an “exhaust”, is arranged at the end. These end components can also be connected to exhaust pipes.
In the case of silencers (also known as mufflers), a distinction is drawn between passive silencers and active silencers. The passive silencers damp the airborne noise transported in the exhaust gas by means of resonance, reflection, expansion and/or absorption effects. In contrast to this, an active silencer operates with active noise control or antinoise, which is produced with the aid of a corresponding electro-acoustic converter, which is generally a loudspeaker. Combinations of active and passive silencers are likewise possible. In the present connection, it should in particular be avoided that an active silencer operates exclusively with antinoise. Rather, in the context of the present invention, an active silencer should optionally be able to comprise properties and/or components of a passive silencer also, such as at least one resonance, reflection, expansion and/or adsorption chamber.
An active silencer can have a silencer housing and at least one electro-acoustic converter arranged in the silencer housing, and at least one connection pipe. The silencer housing can be connected fluidically to the exhaust pipe with the aid of the connection pipe. In this manner, the silencer housing is bypass-connected to the exhaust tract, so the exhaust gas does not flow through it. The fluid connection between the silencer housing and the exhaust pipe, which is created with the aid of the connection pipe, ensures an acoustic coupling for airborne noise, so the noise carried in the exhaust gas can propagate in the direction of the silencer housing, while the noise generated by the electro-acoustic converter can be radiated into the exhaust pipe. A physical distance between the silencer housing and the exhaust pipe is also realised by means of the connection pipe, as a result of which the thermal loading of the converter can be reduced. It has been found, however, that the hot exhaust gases conducted in the exhaust pipe can still result in high thermal loading of the converter. Firstly, the hot exhaust gas can enter the connection pipe and reach the converter by means of diffusion processes. Secondly, the exhaust gas heats up the exhaust pipe, so heat can pass by thermal conduction from the exhaust pipe via the connection pipe to the silencer housing. Finally, thermal radiation can also spread from the exhaust gas or from the exhaust pipe through the connection pipe to the converter.
In order to reduce the thermal loading of the converter and of any electronics of the active silencer arranged in the silencer housing, it is possible in principle to equip the connection pipe with a cooler section between the silencer housing and the exhaust pipe. In this manner, the connection pipe can be cooled in that heat is emitted outwardly via the cooler section. For example, the connection pipe can have outwardly projecting, external cooling ribs in the cooler section. It is likewise conceivable to form a cooling jacket through which a coolant flows in the cooler section. For example, this cooling jacket can be fluidically coupled to a cooling circuit of the internal combustion engine equipped with the exhaust system.